The present invention relates generally to current sensing devices for electrical systems, and more particularly to fault direction indicating alternating current fault indicators.
Various types of fault indicators have been constructed for indicating the occurrence of electrical faults in power distribution systems, including clamp-on type fault indicators, which clamp directly over cables in such systems, and test point type fault indicators, which are mounted on test points in cables or associated connectors of the systems. Examples of such fault indicators are found in products manufactured by E. O. Schweitzer Manufacturing Company of Mundelein, Ill., and in U.S. Pat. Nos. 3,676,740; 3,816,816; 3,906,477; 4,034,360; 4,063,171; 4,086,529, 4,234,847; 4,438,403; 4,458,198; 4,495,489 and 4,794,329 of the present inventor.
In certain applications, such as where two interconnected current sources are present in a single system, it is desirable that a fault indicator, in addition to indicating the occurrence of a fault, indicate the direction of the fault, i.e., whether the fault is upline or downline relative to the location of the indicator on the monitored conductor. On a tie line between two power stations, for example, such direction indications from multiple fault indicators located at spaced locations along the tie line allow the location of a fault along the tie line to be quickly determined and repaired.
The present invention provides a fault indicator which indicates both the occurrence and the relative direction of a fault.
Typically, in a fault indicator detection of fault currents is accomplished by means of a magnetic reed switch or sensing coil positioned in close proximity to the conductor being monitored. Upon occurrence of an abnormally high fault-associated magnetic field around the conductor, the reed switch or sensing coil activates a trip circuit which produces current flow in a trip winding on a magnetic pole assembly which positions a magnetically actuated indicator flag visible from the exterior of the indicator to a fault-indicating position. Upon restoration of current in the conductor, a reset circuit is activated to produce current flow in a reset winding on the pole assembly to reposition the indicator flag to a reset or non-fault indicating position. The invention described in the aforementioned U.S. Pat. No. 4,438,403 provides an improvement in such electromechanical fault indicators, in that it provides a simplified circuit for use in conjunction with a single bidirectional magnetic winding on the pole assembly in place of separate trip and reset windings.
To minimize the power required by the trip and reset circuit in repositioning the electromechanical indicator between reset and trip positions it is desirable that the indicator flag have minimal mass and minimal travel between positions. To these ends a four pole magnetic pole assembly has been used, together with an indicator flag arranged to rotate 90.degree. upon occurrence of a fault, as described in the aforementioned U.S. Pat. No. 4,495,489.
In the aforementioned U.S. Pat. No. 4,063,171 a fault indicator is described which is responsive to fault currents in one direction only, no indication being given for a fault in the other direction or in the absence of a fault current. In U.S. Pat. No. 3,535,593 of the present inventor a power line monitoring device is described wherein the direction of current flow under normal non-fault conditions is indicated by lamps or an electromechanical meter.
In contrast to these devices, the present invention provides a direction-indicating fault indicator having an electromechanical indicator wherein the indicator flag rotates 90.degree. clockwise or counterclockwise from a neutral reset position under the influence of a stationary three pole magnetic pole assembly and a four pole magnetic armature rotatably coupled to the indicator flag, the direction of rotation of the armature being determined by a second pole assembly directionally magnetized by an additional winding to rotate the armature according to the relative direction of the fault.
Accordingly, it is a general object of the present invention to provide a new and improved direction-indicating fault indicator.
It is a more specific object of the present to provide a fault indicator having a compact electromechanical indicator flag assembly for indicating the occurrence and direction of a fault current.